The present invention relates generally to manufacturing of multi-layer ceramic chip carriers and, more particularly, to a method and apparatus for providing uniform axial (uniaxial) load distribution for laminate layers of multilayer ceramic chip carriers.
In the ceramic electronics packaging industry, multi-layer ceramic (MLC) technology is typically used to create three-dimensional circuitry in ceramic chip carriers for microelectronic devices such as integrated circuits and ceramic capacitors. The three-dimensional circuitry in a ceramic chip carrier is made by applying a conductive paste pattern on a ceramic and polymer composite sheet. The ceramic and polymer composite sheet is also known as a “green sheet,” and may also include a number of via holes formed therein in order to allow vertical connection between the conductive paste patterns on adjacent sheets. After the vias are punched, the green sheets are screened and patterned by applying a conductive paste into the via holes and along the surface of the green sheet. The green sheets are then generally stacked in a designated order and laminated together under appropriate temperature and pressure to form a solid laminate. After the stacking and lamination processes, the green laminate is diced into appropriate or functional dimensions for the sintering to form ceramic chip carriers.
FIG. 1 illustrates an existing apparatus and process for stacking and laminating a plurality of individual green sheets 101 to manufacture an MLC green laminate. Because of the differences in loading of the conductive paste 102 (i.e., the differences in the pattern density of paste material) on each green sheet 103, such that the conductive paste loading is lighter at the peripheral areas 104 and heavier in the central areas 105, which results in the pillow-shaped morphology 106 after the stacking of a large number of green sheets.
A typical advanced, high-performance MLC green laminate can include more than 30 layers (even as high as 100 layers) of green sheets having X-Y dimensions of greater than 150 mm×150 mm. Moreover, a typical ceramic green sheet is about 50-500 microns (μm) in thickness, with screen-on conductive paste patterns of about 10-50 μm in height formed upon the green sheet surface. The above described pillow-shaped MLC stack shown in FIG. 1 will then be subsequently compressed under a high compressive force (arrows 107) using the top and bottom steel base plates 108 of the lamination tool such that the entire stack of multi-layered green sheets bonds together to form a solid green laminate.
Unfortunately, due to the pillow-shaped morphology of the green sheet stack, the conductive paste patterns 201 formed along the peripheral areas of the green sheets in the upper portion of the laminate are subject to smearing related damage, as shown in FIGS. 2(a) and 2(b). In particular, the edge smearing damage of the conductive paste patterns results from the unequal shear force between at least two adjacent green sheets present at the pillow-shaped edge area, as opposed to the (solely) vertical compressive stress components present at the center flat area, that are applied to the conductive paste patterns during the highly compressive lamination process. Once the conductive paste patterns are damaged by smear within the green sheet stack (and hence within a green sheet laminate), the sintered MLC chip carriers are considered to be an electrical defect.
Accordingly, it would be desirable to be able to form complex, multi-layer ceramic chip carriers, in a manner that avoids the above described difficulties relating to pillow-effect smearing and damage.